Nitro alcohols are derivatives easily obtained by addition of formaldehyde to nitroparaffins. Several processes have been described to transform them into amino alcohols (alkanolamines) used in the production of cosmetics, detergents or as intermediaries for synthesis of bactericides and pharmaceutical products.
The --NO.sub.2 group can be reduced by the Fe-Fe.sup.++ pair in sulfuric or acetic acid medium, but the weight of reagent used is about three times that of the nitro derivatives to be reduced; a large quantity of solid residue to be eliminated results and it is necessary to rectify the liquid phase containing the amine to obtain a pure product; the yield is on the order of 80%.
A catalytic hydrogenenation can also be performed, for example on Raney nickel in a methanol medium under 60 bars pressure at 40.degree.-45.degree. C. In this case, too, the yield does not exceed 80%; the secondary reactions are numerous, causing the formation of light amines and heavy residue that must be separated from the desired amino alcohol by several successive rectifications which necessitate a large investment and a considerable consumption of energy. On the other hand, the formation of N--CH.sub.3 derivative cannot be avoided, which is then difficult to separate from the desired amino derivative.
An electrochemical reduction process has already been described in U.S. Pat. No. 2,485,982 according to which the operation is in a hydrochloric or sulfuric aqueous solution in an electrochemical cell equipped with a porous porcelain diaphragm. An aqueous solution of hydrochlorides or of sulfate of amino alcohol is obtained that must then be neutralized and/or precipitated to obtain the amine. In addition to the raw material nitro derivative, the acid and the reagents for neutralizing and precipitating are consumed that must then be discharged into the environment.
A reduction process by electrochemical means in a sulfuric acid medium has been sought making it possible to obtain on the one hand a concentrated aqueous solution of pure amino alcohol and on the other hand sulfuric acid solutions that can be reused in the following operation.